Automotive turbine engine

ABSTRACT

Gas flow through a turbine is divided, with part of the flow directed to the compressor for the combustion chamber and part directed to the primary power turbine. Division of the gas flow is accomplished by a mixing wheel of novel design. Before passing to the primary power turbine the gas flow passes through a secondary power turbine that drives the compressor for the combustion chamber. Both the secondary power turbine and the compressor rotate independently of the main turbine rotor shaft. The power input to the secondary power turbine is varied in accordance with the pressure differential between the gas pressure at the outlet of the compressor for the combustion chamber and the outlet from the mixing wheel. If the speed of the main turbine shaft slows down more power is put into the secondary power turbine and the combustion chamber compressor is speeded up so as to produce a higher gas pressure than would otherwise be the case.

United States Patent [191 Wirth et a1.

[ NOV. 13, 1973 AUTOMOTIVE TURBINE ENGINE [76] Inventors: Richard E.Wirth, 1574 Melba Court, Mountain View, Calif. 94040; Manfred N. Wirth,1021 Heatherstone Way, Sunnyvale, Calif. 94087 1 22 Filed: Nov. 19, 197021 Appl. No.: 91,092

[52] U.S. Cl 60/39.17, 60/3925, 60/3952 [51] Int. Cl. F02c 9/08 [58]Field of Search 60/3925, 39.16, 60/3952, 39.18, 39.17

[56] References Cited UNITED STATES PATENTS 2,621,475 12/1952 Loy60/3952 3,500,636 3/1970 Craig 60/3925 2,626,502 1/1953 Lagelbauer.60/39.]6 3,508,395 4/1970 Sebestyn 60/3925 3,609,967 10/1971 Waldmenn...60/3916 3,300,966 l/1967 Chadwick 60/3925 FORElGN PATENTS ORAPPLICATIONS 517,919 3/1953 Belgium ..'60/39.16

Primary Examiner-Carlton R. Croyle Assistant Examiner-Warren OlsenAttorney-John R. Murtha [57] ABSTRACT Gas flow through a turbine isdivided, with part of the flow directed to the compressor for thecombustion chamber and part directed to the primary power turbine.Division of the gas flow is accomplished by a mixing wheel of noveldesign. Before passing to the primary power turbine the gas flow passesthrough a secondary power turbine that drives the compressor for thecombustion chamber. Both the secondary power turbine and the compressorrotate independently of the main turbine rotor shaft. The power input tothe secondary power turbine is varied in accordance with the pressuredifferential between the gas pressure at the outlet of the compressorfor the combustion chamber and the outlet from the mixing wheel. If thespeed of the main turbine shaft slows down more power is put into thesecondary power turbine and the combustion chamber compressor is speededup so as to produce a higher gas pressure than would otherwise be thecase.

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SHEET u or 5 INVENTORS RICH/1K0 E. W/RTH N. IKTH THEIR ATTUKNEY PATENTEDNOV 1 3 I975 SHEET 5 or 5 INVENTOR5 ARD E. W/KT'H ED N. 'W/RT TAEII?ATTOKNEKH KICH MA I Er E AUTOMOTIVE TURBINE ENGINE The invention relatesto turbine engines and more particularly to an improved turbine engineconstruction which will permit the main turbine to run efficiently athigh or low speeds and at varying power outputs such as thoseencountered, for example, in the operation of an automobile.

To be efficient, any engine operation on a thermodynamic cycle shouldutilize as much as the heat generated by the combustion of the fuel asis possible. Maximum utilization of combustion heat occurs when theexhaust temperature of the combustion gases after expansion approachesatmospheric temperature. High efficiency in a turbine engine requiresthat the gas pressure of the combustion gases with respect to the gastemperature prior to expansion be such that, upon the subsequentexpansion of the combustion gases, the exhaust temperature of thecombustion gases will approach atmospheric temperature as closely aspossible.

Combustion pressure in a turbine engine varies as the square of thechange in speed. Any reduction in speed, therefore, causes a muchgreater reduction in gas pressure. Because of this relationship, anysignificant reduction in turbine speed is followed by an excessive dropin gas pressure. The excessive drop in gas pressure means that anefficient ratio of gas pressure to gas temperature cannot be maintained.Expansion of the combustion gases in such case fails to utilize a largeamount of the heat available and the exhaust temperature of the gasesremains high and does not approach atmospheric temperature. Theefficiency of the engine falls off appreciably so much so as to precludethe use of the engine in certain applications where it might otherwisebe advantageous.

Accordingly, turbine engines heretofore have been primarily utilized inapplications where the power demands on the engine are fairly constant.Such applications permit the engine to be run with relatively few speedchanges and, hence, at relatively high efficiencies. Where, however, thepower demands of a particular application such as that of powering anautomobile, vary significantly, the drop in the efficiency of theturbine engine which accompanies significant speed changes has precludedthe use of turbine engines in such applications.

The present invention has for its object an improved turbine engineconstruction which will permit the engine to be run efficiently over awide range of speed changes so that the engine may advantageously beused in applications with varying power output demands.

One manner in which the invention may be practiced is shown in theaccompanying drawings and will be described in the detailed descriptionwhich follows. It is to be understood, however, that the followingdetailed description, and the drawings, are by way of illustration onlyand are not intended to restrict or define the invention, the claimsappended hereto, together with their lawful equivalents, being reliedupon for that purpose.

Of the drawings:

FIG. 1 is a schematic diagram showing the general configuration of theturbine engine;

FIG. 2 is a pressure-volume diagram illustrating the working process ofthe engine;

FIG. 3 is a side elevational view, partly in section, of a turbineengine constructed in accordance with the teachings of the invention;

FIG. 4 is a sectional view taken along the line 44 in FIG. 3, looking inthe direction of the arrows;

FIG. 5 is a sectional view taken along the line 55 in FIG. 3, looking inthe direction of the arrows;

FIG. 6 is an enlarged, detailed view of the secondary power turbine andits associated, variable inlet vanes;

FIG. 7 is an enlarged detailed view, partly in section, showing thearrangement of the inlet vanes relative to the secondary power turbine;

FIG. 8 is a view similar to that of FIG. 7, showing the inlet vanes in adifferent position; and

FIG. 9 is a detailed view, partly in section, showing the differentialpressure-sensing device.

The turbine engine construction of the present invention utilizes a mainor primary air compressor, a mixing wheel and a primary power turbine,all arranged on a main turbine rotor shaft. As shown in the accompanyingdrawings the air compressor may be operated in a single stage withoutcooling devices. It may also be operated in multistages and withintermediate cooling. A combustion air compressor and its associatedsecondary power or drive turbine are also provided and both are soarranged as to be rotatable independently of the main turbine shaft andits rotary components. This arrangement may take many forms. In the formof the invention shown in the drawings the combination air compressorand its driving turbine are mounted on an independently rotatable spoolshaft which surrounds the main turbine shaft.

At the inlet to the secondary power turbine variable inlet vanes are soprovided as to variably control the angle of attack of the gas flowagainst the turbine blades and consequently the rotational speed of theturbine. The actuating mechanism for the inlet vanes responds to adifferential pressure-sensing device which senses the pressure ratio ofthe mixing wheel output pressure to the combustion air compressor outputpressure. This pressure ratio varies inversely with the rotational speedof the secondary power turbine. At low mixing wheel speeds, with theattendant drop in pres sure, the inlet vanes of the secondary turbineare adjusted so as to speed up the secondary turbine and the combustionair compressor which it drives. At high mixing wheel speeds (andpressures) the vanes are adjusted to decrease the speed of the secondaryturbine and combustion air compressor.

The present turbine engine construction employs a differential fluidflow system with two gasifier sections. One gasifier section is made upby the main air compressor, the combustion air compressor and itssecondary drive turbine and the combustion chamber of the turbine. Thisgasifier section is a high pressure system with a relatively small flow.It discharges hot combustion products at high velocity into the othergasifier section, the mixing wheel. The mixing wheel makes up a lowpressure system with a large gas flow. The air-gas mixture dischargedfrom the mixing wheel forms the fluid flow for driving the secondary andprimary power turbines. With the exception of the mixing wheel, which isof the centrifugal impeller type, all compressor or turbine componentsmay be either of the axial or radical type and may be either single ormultistage.

Reference will first be made to FIG. 1 for a general description of anexemplary turbine engine. The engine comprises a single shaft,radial-type, gas turbine with five rotors. Three of the rotors aremounted on a main turbine shaft 10. These rotors are the main aircompressor 12, the mixing wheel 14 and the primary power turbine 26. Theother two rotors rotate on a spool shaft 18 which fits around a portionof the main turbine shaft and which is independently rotatable withrespect thereto. These rotors are the combustion air compressor 20 and asecondary power turbine 22 which constitutes the driver for thecombustion air compressor. A can type combustion chamber 24 is providedfor the turbine and has an air cooled outlet nozzle 26. The outletnozzle 26 directs the combustion gases to the mixing wheel 14 where theyare mixed with incoming compressed air. From the mixing wheel 14 the gasmixture passes to the secondary power turbine 22. The amount of powerdeveloped at this turbine is variable and is controlled so as tomaintain the combustion air compressor 20 at a speed which will developa desirable ratio of gas pressure to gas temperature in the combustiongas. Thereafter the gas mixture passes to the primary power turbine.Expansion of the combustion gases in the primary power turbine 16proceeds to a point where a terminal temperature approaching that ofatmospheric is achieved. The power output thereby developed in the mainturbine shaft 10 is then passed on to an output shaft 28 through asuitable gear train 30 which steps down the high speed of the turbineshaft to'the desired speed at the latter shaft.

The working diagram of the turbine engine is shown in FIG. 2. Line 1-2represents the compression which takes place in the main air compressor.This compression may be polytropic, that is, without intercooling ornear isothermal with intercooling. The line 2-3 represents furthercompression in the mixing wheel. Line 34 represents the division of thegas-flow which occurs when part of the air is conveyed to the combustionair compressor, to be super compressed. This compression is representedby the line 4-5. The major part of the compressed air is trapped in themixing wheel 14. Line 5-6 represents fuel-air combustion in thecombustion chamber, as well as the combustion-gas mixture with thetrapped air in the mixing wheel. The final line 6-1, represents theadiabatic expansion of the combustion gases through the secondary andprimary power turbines.

The combustion gases exiting from the combustion chamber 24 are mixed inthe mixing wheel 14 with the abs. mix temp. Tm mix press. p.m. abs.temp. of the mixing air Ti mixing air press. p.i.

From the above equation it is clear that the mixing pressure is equal tothe mixing air pressure of the gas medium times the ratio of the mixturetemperature to the mixing air temperature:

pm pi(Im/Ti) If the weight of the combustion gases is represented 03 andGi represents the weight of mixing air trapped in the mixing wheel, thenthe heat in the combustion gases may be represented by the formula:

wherein cg is equal to the specific heat of the combustion gases and tgis equal to the temperature of the combustion gases and ta is thetemperature of the atmospheric air.

If the heat energy given off during the flow into the mixing chamber inthe form of work, that is to the blades, be disregarded, the quantity ofheat given off to the compressed mixing air may be expressed as:

Qm Gg X cg (tgtm) Qm is the heat that raises the temperature andpressure in the mixing chamber. It may also be expressed From theselatter two equations, the mixing ratio can be stated as:

wherein ci is equal to the specific heat of the compressed mixing air.

Reference will now be had to FIG. 39 for a detailed description of theconstruction features of an exemplary turbine engine.

For ease of access the outer casing 32 of the turbine is formed in aplurality of removable sections which are bolted together at the flanges34,34. An annular air filter 36, in combination with a dome-like noisesuppressor 38, is provided at one end of the turbine casing. The airfilter surrounds the outwardly flaring mouth section 40 of the air inletfor the main turbine air compressor. The main turbine air compressor 12may be single or multi-stage and may be of the centrifugal, or axialtype, or of any other suitable type. It may also be made with or withoutcooling means. As shown, the compressor comprises a centrifugal impeller42 of customary configuration and is mounted on the leftward end (asshown in FIG. 3) of the main turbine shaft 10. A selfadjusting labyrinthtype seal 44 is provided to prevent interstage leakage along the turbineshaft.

Initial compression of the air takes place in this air compressor stage12. The compressor stage then discharges the compressed air into acircumferential duct 46 formed in two of the sections of the outercasing 32 of the turbine. The circumferential duct 46 conducts thecompressed air to the mixing wheel 14. Before entering the rotatingmixing wheel 14 the air must pass through an air inlet valve plate 48.As will be best seen by reference to FIG. 4, the air inlet valve plate48 is stationary and provides a partial annular opening 50 for thepassage of air for only one-half of its circumferential extent, theother half of the annular opening being blocked off by a wall segment52. Passage of compressed air into the mixing wheel 14 can take place,therefore, only through approximately 180 of mixing wheel rotation.

A can-type combustion chamber 24 (FIG. 4) is positioned at one point onthe periphery of the mixing wheel. The outer casing 54 of the combustionchamber 24 is of generally cylindrical configuration and has a removableclosure plate 56. A fuel injection nozzle 58 is provided on the centralaxis of the chamber and protrudes inwardly of the closure plate 56through an opening 60 formed therein. An inner wall 62 defines an airpassageway which completely encompasses the perforated combustionchamber wall 64. A large air inlet opening 66 is formed at the outer endof the chamber wall 64. The opening 66 also provides access for a sparkplug 70 that is mounted on the closure plate 56. The inner end of thecombustion chamber 24 is formed by a casing 72 that tapers inwardly soas to form the throat of a nozzle 26 for the combustion gases. Airopenings 74,74 are provided in the nozzle casing 72 but these openingsare less numerous than the opening in the combustion chamber wall 64. Agradually flaring casing 76 defines a nozzle diffuser section 78 thatguides the combustion gases to the mixing wheel 14. Stationary guidevanes 80,80 direct the flow of combustion gases into the wheel at thedesired angle of attack.

The configuration of the mixing wheel 14 is believed to be novel. Aspreviously mentioned the inlet to the mixing wheel is controlled by theinlet valve plate 48 so that compressed air from the main air compressorenters the mixing wheel during'only about 180 of the wheels rotationaltravel. The entering air undergoes further compression in the mixingwheel 14 and some of this air is discharged into a passageway 84 thatleads to the combustion air compressor 20. To this end a dividing baffle82 extends inwardly from one side wall of the casing 54 for thecombustion chamber 24 to a point immediately adjacent the circumferenceof the mixing wheel. This baffle serves to define one side of an airpassageway 84 which surrounds the nozzle difiuser casing 76. The otherside of the passageway 84 is formed by duct sheeting 86 which directsthe air past the diffuser casing 76 and into a conduit that leads to thecombustion air compressor 20.

The combustion gases from the combustion chamber are discharged at highvelocity into the chambers 88,88 formed between the blades 90,90 of themixing wheel 14. There the combustion gases mix with the relatively coolair that is trapped between the blades when the blades, during therotation of the mixing wheel, come opposite the discharge nozzlediffuser section. This mixing process occurs with constant volumebecause of the closure provided by the wall segment 52 of the air inletvalve plate 48. For approximately 180 of rotation the vanes 90,90 of themixing wheel 14 communicate with 'a circumferential duct 92. Thecombustion gases mix with the compressed air trapped between the vanes90,90 of the mixing wheel. A transfer of heat takes place and thetemperature of the compressed air is significantly increased. Thisincreased temperature further raises the pressure of the air since theclosure of the wall 52 prevents any expansion thereof. The pressure ofthe air-gas mixture is, thus, raised to a high value as it passesthrough that portion of mixing wheel rotation blocked by the closurering 49 located adjacent the outer circumference of the mixing wheel.

As the air-gas mixture clears the end of the closure ring 49, it isdischarged at high velocity into the first two chambers 51a and 51b.Further discharge of the air-gas mixture into the remaining chambers53,53 occurs as the wheel continues to rotate, however, the discharge ofthe mixture is the result of a scavenging action of the incomingcompressed air. As the combustion gas-air mixture is discharged intothis circumferential duct a limited expansion of the gas mixture takesplace. The duct 92 then conveys the gas mixture to the variable inletvanes 94,94 of the secondary power turbine 22 which serves to drive thecombustion air compressor 20.

As previously stated the combustion air compressor 20 and its associatedsecondary power turbine drive 22 are mounted on an independentlyrotatable spool shaft 18 which surrounds the main turbine shaft 10 (FIG.6). A bearing housing 96 is located between the compressor 20 andturbine 22 and a pair of ball bearings 98,98 are mounted on the housing.In turn, an annular disc 100 is secured to a mounting ring 102 and theassembly of disc 102 and ring 100 mounted on the ball bearings 98,98.The outer circumference of the annular disc 100 is formed with aplurality of equally spaced radial slots 104,104, there being one radialslot 104 for each variable inlet vane 94.

As is best seen in FIGS. 6, 7 and 8, each variable inlet vane 94 isprovided with a pin 106,106 at the inner end of the vane and the ends ofthe pin are pivotally mounted in the duct casing 108 so as to form anaxis about which the inlet vane 94 may be turned or rotated. A secondpin 110,110 is provided for each vane 94 and is positioned in the vaneat its thickest part. This second pin 110 extends through an accessopening 112,112 in the wall 114 of the duct 92 and into one of theradial slots 104 formed in the periphery of the annular disk 100.Lateral rotational movement of the disk 100 moves the second pin 110relative to the first pin 106 and varies the inclination of the inletvane 94 relative to the turbine vanes 116,116.

Lateral or rotational movement of the disk 100 is effected by aconnecting rod 118.'One end of the connecting rod 118 is secured to astud 120 on disk 100. The opposite end 122 of the connecting rod 118extends through the turbine casing 32 and gas duct 92 into a pressuredifferential sensing device 124. The sensing device 124 is secured tothe outer wall 32 of the circumferential duct 92 between the dischargefrom the mixing wheel and the inlet to the secondary power turbine. Asteel bellows 126 is mounted internally of the sensing device ingas-tight relation with the duct 92. The interior space 128 of thebellows 126 is open and subject to the gas pressure in the duct 92. Theopposite end 122 of connecting rod 118 is suitably fixed, in a gas-tightmanner, to the outer end 130 of the steel bellows 126. A biasing spring132 is positioned between the outer end 130 of the bellows 126 and theinner end 134 of the sensor housing 136. The space 138 within the sensorhousing 136 surrounding the bellows 126 is communicated with the duct 46surrounding the combustion chamber 24 through a conduit 140. In this waya pressure differential is applied across the-bellows. The internalspace 128 within the bellows 126 is subject to the gas pressure in theduct 92 leading away from the mixing wheel 14 while the surroundingspace 138 outside the bellows 128 is subject to the discharge pressureof the combustion air compressor 20.

As will be explained more fully hereafter, the pressure differentialacross the bellows 126 serves to adjust the attitude of the inlet vanes94,94. When the bellows 126 is moved outwardly the connecting rod 1 18is likewise moved in the same direction with a resultingcounterclockwise movement of the annular disk (as seen in FIG. 5). Thecounterclockwise movement of the disk 100 moves the pins on the vanescounterclockwise. When the vanes 94 are moved counterclockwise, theangle of attack of the inflowing gases is increased and the secondarypower turbine 22 will accelerate to a higher speed. Clockwise movementin the system decreases the angle of attack of the inflowing gases andthe turbine slows down.

The partially expanded gases from the secondary power turbine 22 areconveyed by a duct 142 to the inlet blades 144,144 of the primary powerturbine 16. These inlet blades 144,144 are arranged around thecircumference of the turbine rotor 16 and direct the gas mixture at theblades 146,146 of the turbine 16 at the desired angle. As the gasmixture passes through the blades 146 of the turbine 16, it expandsagain to approximately atmospheric pressure. The exhaust gases aredischarged from the turbine 16 through a circumferential duct 148 intothe atmosphere.

The operation of the engine and the differential pressure control sensormay be shown by an example:

Assume the engine is designed to run at 40,000 RPM and when running atthis speed will generate a gas pressure of 88 PSIA at the outlet of themixing wheel 14. Compressed air leaves the mixing wheel 14 through theconduit 46 and passes to the combustion air compressor 20 where it isfurther compressed to the end pressure desired in the combustion chamber24. At the same time, the gas mixture generated in the mixing wheel 14passes through the duct 92 to the variable inlet vanes 94 at thesecondary power turbine 22 which drives the combustion air compressor20. Since the pressure of the gas mixture at the outlet of the mixingwheel is communicated with the internal space 128 inside the bellows 126in the sensor housing 136, this pressure exerts an outwardly actingforce which, in conjunction with the bias force of the spring 132, movesthe bellows 126 to its fully extended position. In this extendedposition the connecting rod 118 holds the annular disk 100 in themaximum counterclockwise position. The variable inlet vanes 94 will,accordingly, be positioned to direct the inflowing gases at the turbine22 with a maximum angle of attack.

Inasmuch as the angle of attack of the inflowing gases is at a maximum,the speed of the turbine 22 will increase and so will the speed of thecombustion air compressor 20 which it drives. The combustion aircompressor 20 will generate an increase in air pressure proportional tothe square of the speed increase. This higher pressure will becommunicated so the space 138 surrounding the bellows 126 and acts tomove the bellows inwardly. Inward movement of the bellows 126 moves thevariable inlet blades 94 in a clockwise direction. The angle of attackof the incoming gases is decreased and the speed of the turbine 22decreases. It continues to decrease until the outlet pressure of thecombustion air compressor reaches 132 PSIA. At this point the pressuresin the sensor are balanced.

By selecting the proper spring rate and the pretension of the biasingspring 132 in the sensor, a balance of the system can be achieved at anydesired combustion air pressure.

When it is desirable or necessary to run the engine at a lower or idlingspeed, the fuel control (not shown) to the combustion chamber 24 isadjusted to cut down on fuel. The heat output and temperature of thecombustion gases are reduced correspondingly. This reduces the powerinput and results in a slowing of the main turbine shaft 10. With thefall off in speed there is a sharp the bellows 126 will be extendedoutwardly since the bias force of the spring 132 remains the same. Thesensor will, accordingly, take a new balanced position by adjusting thevariable inlet vanes 94 so as to drive the turbine fast enough toproduce a balancing pressure at the combustion air compressor.

For example, if the cross sectional area of the bellows is one squareinch, the gas pressure at the design speed of 40,000 RPM will exert anoutward force of 88 pounds on the bellows. The combustion air pressurewill exert an inwardly directed force of l32 pounds. Since the sensor isin balance at this point, the bias spring and the spring force of theconvolutions of the bellows exert a force equal to the difference, or 44pounds. When the lower speed of the turbine produces a pressure drop toa pressure of 20 PSIA at the outlet of the mixing wheel, the totaloutward working forces on the bellows is 64 pounds (20 44). Thecombustion air pressure will have to be 64 PSIA to balance this outwardforce. Accordingly, the variable inlet vanes adjust automatically toincrease the angle of attack of the inflowing gases to the point wherethe secondary power turbine drives the combustion air compressor at thatspeed which generates an outlet pressure of 64 PSIA.

The heat output and combustion gas temperature at this lower speed issuch that a combustion gas pressure of 64 PSIA at the subsequentexpansion in the succeeding stages will reduce the temperature of theexhaust gases to nearly ambient temperature. Thus, while the turbinewould be running at a lower speed and with a reduced power output, theefficiency of the engine would be approximately as high as usual.

We claim:

1. A gas turbine, comprising in combination,

a. a main rotor shaft,

b. a primary compressor and a primary power turbine mounted on said mainrotor shaft,

c. an auxiliary rotor shaft independently rotatable of said main rotorshaft,

(1. a secondary compressor and a secondary turbine mounted on saidauxiliary rotor shaft, said secondary compressor being driven by saidsecondary turbine,

e. a combustion chamber,

f. conduit means communicating the output of the secondary compressorwith the inlet of the combustion chamber,

g. means communicating the outlet of the combustion chamber with theinlet of the primary turbine,

h. means dividing the fluid flow from the outlet of the primarycompressor, said means sending a portion of said flow to the inlet ofthe secondary turbine and another portion of said flow to the inlet ofsaid secondary compressor,

i. variable control means for varying the speed of the secondaryturbine, and

j. means for sensing pressure at the outlet of the combustion chamberand at the inlet of the secondary turbine, said sensing means beingconnected to said variable control means whereby the speed of saidsecondary turbine is varied in accordance with the pressure valvessensed.

2. A gas turbine according to claim 1 wherein said dividing meanscomprises a mixing wheel mounted on said main rotor shaft which mixesthe combustion gases from the combustion chamber with the compressedfluid from the primary compressor.

3. A gas turbine according to claim 2 wherein said pressure sensingmeans senses the differential between the pressures at the outlet of thecombustion chamber and at the outlet of the mixing wheel and moves saidvariable control means to operate said secondary power turbine at aspeed which causes the secondary compressor to maintain an efficienttemperaturepressure relationship between the output pressures of saidcombustion chamber and said mixing wheel.

4. A gas turbine according to claim 3 wherein said mixing wheelcomprises a centrifugal impeller and the combustion gases from thecombustion chamber are discharged radially inwardly of said mixing wheelimv the gases striking the blades may be varied.

1. A gas turbine, comprising in combination, a. a main rotor shaft, b. a primary compressor and a primary power turbine mounted on said main rotor shaft, c. an auxiliary rotor shaft independently rotatable of said main rotor shaft, d. a secondary compressor and a secondary turbine mounted on said auxiliary rotor shaft, said secondary compressor being driven by said secondary turbine, e. a combustion chamber, f. conduit means communicating the output of the secondary compressor with the inlet of the combustion chamber, g. means communicating the outlet of the combustion chamber with the inlet of the primary turbine, h. means dividing the fluid flow from the outlet of the primary compressor, said means sending a portion of said flow to the inlet of the secondary turbine and another portion of said flow to the inlet of said secondary compressor, i. variable control means for varying the speed of the secondary turbine, and j. means for sensing pressure at the outlet of the combustion chamber and at the inlet of the secondary turbine, said sensing means being connected to said variable control means whereby the speed of said secondary turbine is varied in accordance with the pressure valves sensed.
 2. A gas turbine according to claim 1 wherein said dividing means comprises a mixing wheel mounted on said main rotor shaft which mixes the combustion gases from the combustion chamber with the compressed fluid from the primary compressor.
 3. A gas turbine according to claim 2 wherein said pressure sensing means senses the differential between the pressures at the outlet of the combustion chamber and at the outlet of the mixing wheel and moves said variable control means to operate said secondary power turbine at a speed which causes the secondary compressor to maintain an efficient temperature-pressure relationship between the output pressures of said combustion chamber and said mixing wheel.
 4. A gas turbine according to claim 3 wherein said mixing wheel comprises a centrifugal impeller and the combustion gases from the combustion chamber are discharged radially inwardly of said mixing wheel impeller.
 5. A gas turbine as set forth in claim 4 wherein the combustion gases are mixed with air in said mixing wheel at constant volume and then discharged to the secondary and primary power turbines.
 6. A gas turbine as set forth in claim 5 wherein said secondary power turbine comprises a plurality of radially disposed blades and said variable control means comprise adjustable inlet vanes adjacent the outer periphery of said blades whereby the angle of attack of the gases striking the blades may be varied. 